One of the great accomplishments of public health in the US is simply the existence of the thing in the first place. That is, Americans actually know something about our health on a population level. We take the availability of statistics and health data for granted; every day we read about the 80 million Americans with heart disease or the 8 million with diabetes and we don't really consider where those numbers come from. The significance of this information was highlighted for me last year, when I spoke with Christopher Murray, now the director of the University of Washington's Institute for Health Metrics and Evaluation. Funded by a $105 million grant from the Gates Foundation, the Institute follows a simple idea: If we want to improve health, we have to have a baseline understanding of what health is, and a scientific understanding of what works. Unfortunately, in most of the world, Murray notes, there's little knowledge about the most basic measures of health: mortality rates, birth rates, morbidity rates - these measures that we in the US take for granted remain question marks in many parts of the world.

So how is it that we know this stuff in the US? What mechanisms do we have for getting these numbers and validating their accuracy? Basically, the Centers for Disease Control and Prevention goes out and counts.

I was reminded of all this yesterday when I was walking along San Francisco's Embarcadero to visit the Ferry Building with my son. Right there on the Embaradero are four semi trailers, with the CDC logo and the words "National Health and Nutrition Examination Survey." Here's a picture (that's the Bay Bridge in the background):

Walking over, I thought this might be a kind of Bookmobile for health, where you can stop by and get some pamphlets or something. They weren't open, though, so I had to go online this morning to figure out what NHANES is all about. Turns out this is a much bigger operation than I'd thought. Turns out the survey has been going on since the early 1960s and has logged over 140,000 examinations. That's right, examinations. Here's a diagram of what's inside those semi-trailers:

So it's not a drop-in center at all; the CDC decides to visit an area, then plops its trailers in a central location and mails invitations to various people, based on demographic surveys. Though the CDC points out that this isn't a substitute for a regular doctor's exam - indeed, the tests aren't usually part of a standard physical - the information is useful for individuals, including results of STD tests, bone-density measures, kidney function tests, pregnancy tests, toxic exposures, and so on. Exactly which tests somebody will get depends on their age, sex, and so forth. Here's a video tour of the trailers: link

What comes out of NHANES are many of the metrics that pop up all the time: as the CDC says, "NHANES data have been used to influence policy and improve the health of the U.S. population in many ways including: getting lead removed from gasoline; creating and updating the pediatric growth charts; and establishing national baseline estimates for cholesterol, blood pressure, and Hepatitis C in the U.S." It all gets funneled over to the National Center of Health Statistics.

This is by no means sexy stuff; but it is a window into the workhorse engine of public health that is the CDC. Basically, what happens in these trailers becomes the baseline for our national health policy. It sets the yardstick for the state of our national health, and lets CDC researchers - and anyone else who wants a look at the data - evaluate how our health might be changing, for the good or the worse.

I don't mean to overdo it, but I find this pretty impressive. Even as so many people out there, including me, shake the trees for new tools that will let us measure our health in new ways - stuff like assessing our genetic risks to using proteomic technology for early detection of disease - it's worth remembering that it still takes a lot of work and money just to measure the simple stuff.

I'm gonna see if I can't get a tour from the CDC and follow up when the trailers open in a couple weeks.